How to get to Citadel Early- Fallout 3
Disclaimer:
This glitch requires you to have 5 locations on your Pip-Boy 3000 (you need this to fast-travel out of the Citadel.) From Vault 101: Springvale Springvale Elementary Megaton Citadel.
The Citadel is useful because you can get Power Armour (no helmet) and Power Armour training. This is important as if you kill any Brotherhood Soldier or Brotherhood Outcast you can use their Armour.
If you have Point Anchorage DLC this is a bit useless as once you complete it you can get Winterized Power Armour and Power Armour training.